Contact material

ABSTRACT

A contact material having a high durability is prepared from an alloy consisting of 45 to 85 percent by atom of palladium and 55 to 15 percent by atom of aluminium.

United States Patent 1191 1111 3,826,886 Hara et al. July 30, 1974CONTACT MATERIAL [56] References Cited [75] Inventors: Toshito Hara,Kawasaki; Hiroaki UNITED STATES PATENTS Tanaka, Yokohamarshmchl2,418,710 4/1947 Hensel 75/172 R Shmwsato, Kawasakl, all of Japan2,787,688 4/1957 Hall et al. 75/172 R x [73] Assigneei Fujitsu Limited,Kanagawa ken 3,428,490 2/1969 Bravo et al 75/172 R x Japan PrimaryExaminer-L. Dewayne Rutledge [22] Flled: 1972 Assistant Examiner-E. L.Weise [211 App]. No.: 241,326 Attorney, Agent, or Firm-Nelson E.Kimmelman;

Maleson Kimmelman Foreign Application Priority Data Apr. 15, 1971 Japan46-23468 [57] ABSTRACT Aug. 30, 197! Japan 46-66425 A contact materialhaving a high durability is prepared from an alloy consisting of to 85percent by atom Cl 5/l R of palladium and 55 to 15 percent by atom ofalumin- [51] Int. Cl. HOlh l/02, C22c 5/00 i [58] Field of Search /172R, 138; 200/166 C 3 Claims, 7 Drawing Figures PATENTEDJULBO m4TEMPERATURE C CONSTITUTION OF Pd-AL ALLOY WEIGHT PERCENT PALADIUM I TOOl 500 I I o|o203o4o5oso7oso9o|oo AL ATOMIC PERCENT PALLADIUM PdPATENTEDJULSO m4 3Q826L886 SHEET 2 OF 3 F/g. 2A

(6OPd-4OAg) Fig. 2C

(PdgAL) Fig. 20

(PdAL) The present invention relates to a novel contact material, moreparticularly, relates to a contact material consisting of apalladium-aluminium alloy and having a high durability.

Electromagnetic relays which include one or more contacts are generallyutilized for electrical machinery and apparatus under low level to highlevel conditions. While electro-magnetic relays having a high durabilityhave heretofore been proposed, such devices have not been foundcompletely satisfactory because of undesirable properties of theconventional contact materials.

Broadly speaking, contact failures may be classified l broadly into twoclasses:

I. increase of contact resistance 2. failure to open. The contactfailures as stated above mainly originate from the following sources,high power conditions not considered,

a. formation of corrosion products such as oxide or sulfide layers whichhave low conductivity on the contact surface,

b. formation of an organic polymer layer which has low-conductivity onthe contact surface,

c. material transfer from one of the contact surfaces to the other, and

d. erosion of the contact material.

Therefore, in order to provide an excellent contact useful forelectrical machinery and apparatus under low level to high levelconditions, it is first necessary to provide a contact material havinghigh resistance against corrosion, material transfer and erosion and lowactivity for formation of organic polymer. Further, it is desirable thatthe contact material has high hardness and melting point.

Generally, conventional contacts are made of gold, silver, platinum,palladium, rhodium, ruthenium, molybdenum, tungusten and alloysincluding one or more of the abovementioned metals. However, it is knownthat although contact material consisting of gold, silver or alloysthereof has a high resistance to corrosion and a low activity forformation of organic polymer, it has undesirably low resistance againstmaterial transfer and erosion. It is also known that contact materialconsisting of a platinum group metal, for example, platinum, palladium,rhodium, ruthenium and alloys thereof, has a high resistance againstmaterial transfer and erosion but it has an unfavourable high activityfor formation of organic polymer. Further, it is known that a contactmaterial consisting of a metal with a high melting point such asmolybdenum, tungsten and alloys thereof has excellent resistance againstmaterial transfer and erosion and a low activity for formation oforganic polymer while it has an undesirable low resistance againstformation of corrosion products.

Generally, intermetallic compounds have a higher hardness and meltingpoint than those of simple metals or nonintermetallic compound alloysbecause the metal atoms in the intermetallic compound are strongly andstably bonded to each other. Accordingly, contact materials consistingessentially of an intermetallic compound have a high resistance tomaterial transfer and erosion. Also, since the intermetallic compoundshave poor chemical activity, contact material consisting essentially ofthem have a poor activity for formation of organic polymer layer and ahigh resistance to corrosion.

Therefore, the intermetallic compounds have an adoptability for thecontact material higher than that of the conventional simple metals oralloys. However, in the case where the intermetallic compound containsno noble metal such as gold, silver and platinum group metals forexample, in the case of tungsten carbide (WC) or nickel tinintermetallic compound (NiSn), such intermetallic compounds have anundesirable high tendency to form a stable oxide film on the surfacethereof in atmosphere. Accordingly, contacts made up of theintermetallic compounds containing no noble metal frequently suffer fromcontact failures and thus can not be used under medium or low levelconditions.

As is clear from the above description, an ideal contact material whichcompletely satisfies all the above stated requirements has not yet beenrealized.

An object of the present invention is to provide a contact materialsatisfying the above-stated requirements that is, having high resistanceto corrosion, material transfer, and low erosion and low activity forformation of an organic polymer layer and thus excellent durability.

The object of the present invention can be accomplished by a contactmaterial composed of an alloy consisting of 45 to percent by mol ofpalladium and 55 to 15 percent by atom of aluminium.

' The features and, advantages of the present invention will be apparentupon reading the following description and inspecting the accompanyingdrawings, in which;

FIG. I is a phase diagram of palladium-aluminium system,

FIGS. 2A, 2B, 2C and 2D are photographs showing the resistance of Pdmetal, Pd-Ag alloy and PdgAl and PdAl compounds to material transfer anderosion,

FIG. 3 is a graph showing'the relationship between cumulative failurerate and number of operations for Pd metal and Pd Al and PdAl compounds,and

F IG. 4 shows a circuit for testing the properties of the contactmaterial.

The palladium-aluminium alloys are prepared by an arc-melting method inwhich a predetermined quantity of palladium (purity: 99.98 percent orhigher) is meltmixed with a balanced quantity of aluminium (purity:99.999 percent or higher) in an electric furnace using a non-consumptiontype tungsten anode in an argon atmosphere.

Referring to FIG. 1, the palladium-aluminium alloy includes threeintermetallic compounds, Pd Al PdAl and Pd Al which have properties asshown in Table l.

Item 3 4 w Table 1 Material ltcm Pd Pd Al PdAl Pd Al Al Annealingtemperature (C) 1200 1300 800 Hardness before annealing 549 Hv 560 Hv672 Hv Hardness after annealing 40 594 Hv 495 Hv 668 Hv l7 23 X-raymicro No No No No No analysis segresegresegresegresegregating gatinggating gating gating Note: Hv Vickcrs hardness number As Table 1 clearlyshows, the compounds Pd Al and PdAl have an extremely high hardness ofabout 500 to 600 Hv. The compound Pd Al has a very porous structurewhich is unsuitable for use as a contact material.

The inventors have discovered that an alloy consisting of 45 to 85percent by atom of palladium and 55 to l5 percent by atom of aluminiumand containing at least one of PdgAl and PdAl, has excellent resistanceto corrosion, high hardness and melting point and low chemical activityfor formation of organic polymer, and therefore is useful as a contactmaterial having high resistance to material transfer and erosion.

For example, a contact made of the material of the present invention canstably retain a low contact resistance even after the contacts areoperated times at a contact force of about 4 g at a drive frequency of1.5 Hz under a contact load of mV 6 mA in air of a relative humidity of80 to 90 percent.

lf palladium in the alloy is in an amount more than 85 percent by atom,the resultant alloy has a undesirable high activity for the formation oforganic polymer on the surface thereof. Also, if the amount of palladiumin the alloy is less than 45 percent by atom, the resultant alloy has alow resistance to corrosion, material transfer and erosion.

FlGS. 2A to 20 show the resistance to material transfer and erosion ofbutton-shaped contact made up of a simple Pd metal alloy consisting of60 parts by atom of Pd and 40 parts by atom of Ag, and intermetalliccompounds consisting of Pd Al and PdAl, respectively.

The button-shaped material was made the cathode and the Pd wire was madethe anode.

After the button-shaped cathodes were brought into contact with theanodes about 10 times under a contact load of V 3 A at a contact forceof 4 g at a drive frequency of 10 Hz hair the appearance of the cathodesand anodes was observed in order to estimate the resistance of thematerials to material transfer and erosion.

Referring to FlGS. 2A and 28, it will be observed that the lower Pdmetal and Pd-Ag alloy cathodes were remarkably eroded and transferred tothe upper Pd metal mode so as to form a projection on the anode.

"a comparison in FIGS? zeaiazniareraaaa and maraerarbaeaaon's saturatedx' ienavaaora e051 parison with Pd metal. The term cumulative failurerate (C.F.R.) used herein refers to the ratio in percent of thecumulative failure number in excess of the failare level 2 w to thecumulative measurement number. The measurement was carried out at acontact force of 4 g, at a drive frequency of 1.5 Hz under a contactload of 20 mV 6 mA. For every material, 5 to 8 samples were measured.

Referring to FIG. 3, in the measurement of the simple Pd metal contact,the number of contact failures increases after the contact numberexceeds 3 X 10 whereas in the measurements of the Pd Al and PdAlcompound contacts, no contact failures are observed even after thecontact number exceeds 10 From FIG. 3, it is obvious that PdgAl and PdAlcompounds have no activity for the formation of organic polymers derivedfrom xylene vapor.

The following examples are intended to illustrate the application of thepresent invention but are not intended to limit the scope thereof.

EXAMPLE I An intermetallic compound PdAl was prepared from 50 parts byatom of palladium (purity: higher than 99.98 percent) and 50 parts byatom of aluminium (purity: higher than 99.999 percent) by arc-meltingthem in a water-cooled copper hearth using a non consumption typetungsten anode in an argon atmosphere for 30 to seconds. The resultantcompound was repeatedly arc-treated in the water-cooled copper hearth onthe alternate surfaces thereof in order to homogenize the internalstructure thereof. The homogenized compound was annealed at l300C for 5to 6 hours.

The annealed compound was formed into a buttonshaped contact strip at500 to 700C.

The resultant contact strip had a hardness of 495 Hv.

The two PdAl contact strips were made the anode and cathode, facing eachother, of an electromagnetic relay in the circuit as shown in FIG. 4.The contacting operation was carried out in air of a relative humidityof to percent.

Even after 1.5 X 10 contactings the PdAl contact showed no contactfailure.

In comparison, a simple silver metal contact showed a cumulative failurerate of about 25 percent at 6 X 10 contactings.

An intermetallic compound PdgA] was prepared from 66.7 parts by atom ofpure palladium and 33.7 parts by atom of pure aluminium by the sameprocedure as Example But the annealing temperature was at 1200C.

The same testing as in Example 1 was applied to the compound Pd Al inair containing 100 ppm. of H S gas and having a relative humidity of 80to 90 percent.

At 1.3 X contactings, the Pd Al contact showed, acumulative failure rateof about 54 percent whereas a simple Pd metal contact showed acumulative failure;

rate of about 64%.

EXAMPLE 3 EXAMPLE 4 An alloy was prepared from 60 parts by atom of purepalladium and 40 parts by atom of pure aluminium by the same method asin Example 1.

The resultant 60 Pd 40 Al alloywas given the same tests as in Example 1in air of a relative humidity of 80 to 9 0 percent ii'v'efirtr 1.4 X l0ope rations, no

contact failures were recorded.

EXAMPLE 5 The same procedure as in Example 1 was repeated using parts byatom of pure palladium and 15 parts ,by atom of pure aluminium. But theannealing temperature was llO0C.

The same testing procedure as in Example 1 was carried out for the above85 Pd 15 Al alloy in air containing saturated xylene vapor. Even after1.0 X 10 operations, the 85 Pd 15 Al alloy contact showed no contactfailures.

In comparison, a Pd 10 Al alloy contact showed a cumulative failure rateof 25 percent at 1.0 X 10 operations.

What we claim is:

1. In an electrical switch having at least one contact, the improvementwherein said contact is composed of an alloy consisting of l from 45percent to 85 percent by atom of palladium and (2) from 55 percent to 15percent by atom of aluminium.

2. An electrical switch as claimed in claim 1, wherein said alloyconsists substantially of an intermetallic compound of the formula: PdAl.

3. An electrical switch as claimed in claim 1, wherein said alloyconsists substantially of an intermetallic compound of the formula:PdAl.

PC1-1050 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent3,826,886 Dated July 30, 1974 Q Toshito Hara et al Inventor-(s) It iscertified that error appears in the aboveidentified patent and that saidLetters Patent are hereby corrected as shown below: C

Page 1 left column fourth line from the bottom, H n1 delete "Aug. 30,1971 Japan .46-66425 I Signed and Sealed this 0 thirteenth Day of April1976 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Altcsn'ng Officer (mmnissium-r uflateirlsand .Tradwnurks

2. An electrical switch as claimed in claim 1, wherein said alloyconsists substantially of an intermetallic compound of the formula:Pd2Al.
 3. An electrical switch as claimed in claim 1, wherein said alloyconsists substantially of an intermetallic compound of the formula:PdAl.